A current trend in polymer chemistry is to control the architecture of polymers produced from a variety of monomers. Group-transfer polymerization (GTP) is a new method of polymer formation that involves the repeated addition of monomer to an initiator to form a polymer with an active terminal group that is capable of polymerizing further in the presence of monomer and catalyst (Webster et al., J. Amer. Soc., Vol. 105, 1983, pp 5706-5708). Use of group transfer polymerization has resulted in processes for producing some unique comb, star and block copolymers. U.S. Pat. Nos. 4,414,372, 4,417,034, 4,508,880, 4,524,196, 4,581,428, 4,588,795, 4,656,233, 4,659,782, 4,659,783, 4,681,918, 4,695,607, 4,711,942 and commonly assigned serial numbers 627,919 filed July 5, 1984, and 771,685 and 771,686 filed Sept. 3, 1085, disclose processes for the "living" polymerization of an acrylic or maleimide monomer in the presence of an initiator. These patents and applications, while they separately mention the possibility of using initiators with more than one initiating site and of monomers with more than one active site, do not teach a GTP-process for producing a ladder polymer using a multifunctional initiator and a multifunctional monomer. In fact, 5,659,783 discloses that mixtures of monofunctional and difunctional monomers under GTP-polymerizing conditions produce gels, indicative of significant cross-linking during polymerization. It is thus surprising and unexpected that difunctional monomers can be used in the process of this invention to produce soluble ladder polymers.
Further, the prior art discloses no processes for preparing ladder polymers from acrylic or maleimide monomers using non-GTP processes.
Overberger et al., Adv. Polymer Sci., Vol. 7, pp 113-150 (1970), review general processes for the formation of several types of ladder polymers and discuss specific examples of each process. However, no example of a "classical ladder polymer" consistent with the definition of ladder polymers of this invention with ester- or amide-containing rungs is disclosed.
Ogata et al., J. Polymer Sci., Part A-1, Vol. 9 (1970), pp 1759-1763, disclose the photopolymerization of hydroquinone diacrylate in solution to give a highly swollen polymeric solid. The polymer is also swelled in dimethylformamide or dimethylacetamide, but is not truly soluble in any solvent. The polymer is degraded by sulfuric acid to hydroquinone and poly(acrylic acid).
Azuma et al., Polymer J., Vol. 4, No. 6 (1973), pp 628-636, disclose the photopolymerization of ortho-, meta-, and para-phenylene diacrylates (PDA). Intermolecular polymerization is favored for meta-, and para-PDA, leading to insoluble, cross-linked polymers. The so-called "ladder-type" polymer produced from ortho-PDA is more accurately described as a linear polymer with pendant macrocycles.
Peterson et al., U.S. 4,284,732, discloses polymers and copolymers based on the unsaturated bisesters of the formula ##STR2## in which R represent hydrogen or a methyl group and X represents chlorine and/or bromine. However, the polymers obtained from these bis-esters by either radical or anionic polymerization are crosslinked insoluble homopolymers or copolymers, not ladder polymers.